How to unwrap a tree trunk?
If you take screenshots from multiple sides and upload them I can just tell you how.

Add a seam everywhere there's a super hard angle between two surfaces, and in UV window unwrap the object. This is super straight forward, tbh. 

On the inside of the piece of wood it doesn't matter too much where you place seams because likely no one will see inside depending on the size of the object. So just place them where most convenient and least likely to produce super obvious seams that aren't possible to hide without being super inconvenient.